Saturday, February 9, 2008

Experimental verification part I - Mental models II

The same applies to every other physics topic - energy, acceleration, momentum, collisions, and many more. Each person has an interior "mental model" of each topic which accounts for a few of its most salient and noticeable characteristics - the things which really grabbed that person's attention. For instance, collisions: tomatoes will splash, balls will bounce, cars will bend and break, glass will shatter. Often the mental model is implicit; perhaps you've never stated or explained it, but you feel confident in applying it to real life collisions and conversing about them. Yet if someone were to engage you in a careful conversation about collisions, even simple things like what happens when a small ball hits a large ball, and what if one is sitting still to start with, or if one ball is catching up with the other one, then if you are like most people then you will run into trouble pretty quickly, and typically without knowing it. Most people will not even be able to correctly describe the details of things that they have experienced thousands of times already - like the trajectory of a ball falling off a table. (If you doubt this, try working through a unit of Physics By Inquiry.) Our mental models are not fundamentally observational or descriptive; neither are they reasoned and self-consistent; instead are functional and confined to only a few broad outlines. I know how to flip a switch; I know that sometimes I need to call an electrician; I know that there are wires and power plants; I know not to touch certain wires; what else do I need to know about electricity?

The problem is not a lack of intelligence - people who do through Physics By Inquiry and reason their way through the questions it asks, with someone to coach them through, develop much more accurate and detailed mental models. Instead the problem is something very human, part of the way we are, the way that we observe the world around us.

The point of this lesson about human nature is that it is perfectly natural that for millennia the human race believed that the universe revolves around the earth, heavy objects fall faster than slow ones, nature abhors a vacuum, and so on. Individually and as a race, we have an unending ability to construct functional but limiting and inaccurate mental models, and then in the face of contrary evidence either justify our models or else just not notice the evidence.

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